Resistance devices for use in energizing the starting winding of a split phase induction motor

ABSTRACT

A resistance device is provided for a split phase induction motor having a main field winding and a starting field winding, said device having a high temperature coefficient resistor adapted to be connected in series with the starting field winding. The device includes two housing halves which accept and locate a disc-shaped positive temperature coefficient resistor and two substantially flat spring contacts.

United States Patent 1191 11 1 3,924,222 Slocum Dec. 2, 1975 1 RESISTANCE DEVICES FOR USE IN [56] References Cited ENERGIZING THE STARTING WINDING UNITED STATES PATENTS OF A SPLIT PHASE INDUCTION MOTOR 3.731752 5/1973 Strachan 318/471 [75] Inventor: Charles W. Slocum, Spring Lake 3,750,082 7/1973 Pete son et al.-

33 /22 Heights, N,J 3,794,949 2/1974 Larsen et al. 1 338/22 R 3,842,188 10/1974 Petersen 174/52 R [73] Assignee: Thermo-Electronics, lnc.,

Allenwood Primary Examiner-Volodymyr Y. Mayewsky [22] Filed: Oct. 9, 1974 1211 Appl. No.: 513,256 [57] ABSTRACT A resistance device is provided for a split phase induction motor having a main field winding and a starting [52] US. Cl 338/220; 174/52 R, 318/471, field winding, Said device having a high temperature I t C1 gig 130 coefficient resistor adapted to be connected in series n u u s u ll t t f d d l d [58] Field 01 Search 338/22 R, 22 so, 220, 252, e S armg Wm mg 6 evlce es 338/276, 322; 219/541, 544, 553; 310/68, 68 C; 318/221 E, 229, 471, 472, 473; 174/52 R;

two housing halves which accept and locate a discshaped positive temperature coefficient resistor and two substantially flat spring contacts.

1 Claim, 12 Drawing Figures 3 225 26 28a 20 I I {F 1 i IL yfl o o 5J6 XI 1 J 1\/ z 1 I' e \VJ' 1 1 246 445 4,95 :82

US. Patent Dec. 2, 1975 FlQll TEMPE/PA TUP RESISTANCE DEVICES FOR USE IN ENERGIZING THE STARTING WINDING OF .A SPLIT PHASE INDUCTION MOTOR BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to improvements in resistance devices for use in the starting winding circuit of a conventional split phase induction motor, and more particularly to such a device employing a high temperature coefficient resistor adapted to be series connected with the starting winding and thereby to energize the starting winding when the resistoris unheated and to deenergize the starting winding when heated by starting current flowing therethrough.

2. Description of the Prior Art Single phase, alternating current induction motors of the distributed winding type conventionally include a main field winding and a starting field winding, the two windings being angularly displaced on a stator core and being energized, respectively, by phased displaced circuits in order to provide starting torque. In one form of single phase induction motors, referred to as resistance-split, the starting winding has a higher impedance than the main winding and may have additional resis-,

tance connected in series therewith, the difference in the impedance of the respective main and starting winding circuits providing the requisite phase-displace, ment. Such additional resistance has previously incontact against the parallel contact surfaces of the recluded a high" temperature coefficient resistor having relatively low resistance during periods of starting but higher resistance a short time later due to the selfgenerated heat in the resistor. Such resistors are commonly referred to as positive temperature coefficient resistors and normally increase in resistance many times upon the heating thereof. Such increased resistance is effective in reducing the current through the starting winding to a low level at which the starting winding is effectively cut out of the motor circuit, the small current drawn being adequate to maintain the high resistance temperature of the resistor.

My co-pending application, Ser. No. 413,839, filed Nov. 8, 1973, is one embodiment of adevice of this type.

SUMMARY OF THE INVENTION In accordance with the broader aspects of this invention there is provided for use in selectively energizing the starting field winding of a split phase induction motor, a positive temperature coefficient resistance device adapted to be series connected with the starting winding. This device includes a two piece housing assembly of dielectric material having matching surfaces between the two pieces and having a cavity therein which opens into the matching surfaces, which includes a cavity portion in both of the pieces, and which includes a pair of receiving surfaces each being disposed parallel to the matching surfaces. I

Each of the two pieces includes a terminal receiving notch in one of the matching surfaces, each terminal receiving notch connecting the cavityito the outside of the housing; and each of the pieces also includes a positioning notch diametrically opposite to the terminal receiving notch being recessed into the cavity portion and into the matching surface thereof.

A curved, leaf spring type, contact is assembled into each housing piece and is located by the respective tersistor. Insulated pigtail leads are attached to each of the contacts and exit the housing by way of the respective terminal receiving notches.

It is an object of this invention to provide a resistance device for use in energizing the starting winding of a split phase induction motor.

It is another object to provide a unitary resistance device which may be conveniently removably connected to the starting winding'terminals of a split phase motor.

It is still another object to provide a unitary resistance device of compact simplified design which may be economically manufactured.

. BRIEF DESCRIPTION OF THE DRAWING The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will .be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings.

FIG. 1 is a top plan view of the assembled device;

FIG. 2 is a front view of the assembled devicetaken substantially as shown by view line 2-2 of FIG. 1;

FIG. 3 is an end view of the assembled device taken substantially as shown by view line 33 of FIG. 2;

FIG. 4 is a top plan view of one piece of the housing taken substantially as shown by view line 4-4 of FIG. 2;

FIG. 5 is a front view of the housing piece of FIG. 4 taken as shown by view line 5-5 of FIG. 4;

FIG. 6 is a top plan view of the device taken substantially as shown by view line 66 of FIG. 2, showing the device with one piece of the housing and one contact removed and showing the location. of the removed contact by phantom lines; x FIG. 7 is a cross-section taken substantially along section line 77 of FIG. 6;

FIG. 8 is a plan viewof one of the contacts of the device;

FIG. 9 is a side view of the contact of FIG. 8;

FIG. 10 is a plan view of the contact of FIG. 8, taken as shown in FIG. 8 but with a pigtail conductor attached;

FIG. 11 is a typical circuit diagram of an induction motor in which the resistance device of this invention is connected; and

FIG. 12 is a graph of temperature versus resistance, showing the temperature coefficient characteristics of the positive temperature coefficient resistor used in the device.

Referring to the drawings, and more particularly to FIGS. 1 through 3, the positive temperature coefficient device "of the present invention includes a housing 20 which includes two identical housing pieces 22a and 22b (except as otherwise shown and described), a pair of insulated pigtails or insulated conductors 24a and 24b, a mechanical clip or spring clip means 26, and a pair of tubular rivets 28a and 28b which secure the metallic clip 26 to the housing pieces 22 and which also secure the housing pieces 22 to each other.

Referring now to FIGS. 4 and 5, the housing piece 22b is shown, the parts thereof identified by numerals with the suffix b being duplicated in housing piece 220.

Each includes a matching surface 30, a cylindrical cavity portion 32, a terminal receiving notch 34 which extends radially from the center of the cylindrical cavity portion 32 outwardly through the matching surface 30, a positioning notch 36 in the matching surface 30, being diametrically opposite to the notch 34, and a pair of holes 38 and 40, one of which is located at an acute angle with respect to the notch 34. The cylindrical cavity portions 32 each include a receiving surface 42 which comprises thebottom of the cylindrical cavity portion 32. As can be seen in FIG. 5, the notches 34 and 36 are of a depth substantially equal to that of the cylindrical cavity portion 32. The housing pieces 22 are preferably molded of an insulating material such as a high temperature phenolic resin.

Referring now to FIGS. 6 and 7, these figures show one of the housing pieces 22b with a contact and pigtail assembly 44b being assembled into the cavity portion 32b and with a disc-shaped positive temperature coefficient resistor 46 being assembled onto the contact and pigtail assembly 44b. FIG. 6 also shows, by phantom lines, the position of a second contact and pigtail assembly 44a as mounted in the housing piece 22a (not shown).

Referring now to FIGS. 8, 9 and 10, and especially to FIG. 8, each of the contact and pigtail assemblies 44 include a spring metal, strip contact 48 of beryllium copper or the like and is of a generally elongated rectangular shape having a pointed or fitted end 50, a reduced width portion, 52 and a lug portion 54. FIG. shows contact and pigtail assembly 44 after the insulation of the pigtail 24 has been stripped from a stripped end portion 56 thereof and the lug portion 54 has been swaged around the stripped end portion 56 to provide electrical and mechanical connection between the pigtail 24 and the contact 48 and to provide a reduced width terminal means 58.

Referring to FIG. 6, the contact and pigtail assembly 44b is shown installed in the housing piece 22b with the terminal means 58b being inserted into the terminal receiving notch 34b and with the pointed end 50b being inserted into the tapered positioning notch 36b. Since it is clearly seen that the contact 48b is of a substantially rectangular shape, having a width greater than the width of the notch 34b, it can be seen that the notch 34b, the notch 36b, the reduced width of the terminal means 58b, the pointed or fitted end 50b, and the width of the contact 48b intermediate of the pointed end 50b and the terminal means 58b cooperate to provide contact positioning and terminal access means for rectilinear positioning and for securing of the contact 48b in the housing 22b and for providing electrical access to the contact 48b. I

Referring now to FIGS. 7 and 9, FIG. 9 shows the initial bowed contour of the contacts 44 which provide spring .means for resiliently urging contacts 48 into electrical conducting engagement with the positive temperature coefficient resistor 46. Referring to FIG. 7, the contact and pigtail assembly 44b is shown installed into the housing piece 22b with the contact 48b partially straightened from its initial condition as it is when the contact 48b is in its completed assembly. Abutting the contact 44b is the positive temperature coefficient resistor 46 having parallel disposed contact surfaces 60a and 60b which are preferably formed of silver.

Referring again to FIG. 6, it can be seen that when the other housing piece 22a is placed on top of the housing piece 22b that the other contact and pigtail assembly 44a will be located as shown by the phantom lines; so that theterminal means 58a is insulatingly separated from the terminal means 58b and the contact 48a engages the other resistor surface 60a in the same manner as contact 48b.

The positive temperature coefficient resistor 46 is of a disc-shape and is of the type conventionally used in connection with split phase motors and has a relatively low resistance at room temperature but higher resistance at the higher temperatures produced from heating with the passage of current therethrough.

Referring now to FIG. 1 1, a typical split phase motor, which includes the present invention, comprises: a rotor 62, a stator windin g 64, a starting winding 66, the resistor 46, and a pair of motor terminals 68a and 68b.

In operation, upon the application of power to the motor terminals 68a and 68b, assuming the resistor 46 to be at room temperature, relatively high current is drawn therethrough by the starting winding 66 thereby producing starting torque for the motor. This current causes internal heating of the resistor 46 thereby increasing the resistance of the resistor 46 which in turn reduces the current flow. When the resistance of the resistor 46 reaches a suitably high value and the starting current to the starting winding 66 correspondingly drops, a condition is reached of which the current flow through the winding 66 is insufficient to sustain energization, which, for all practical purposes, removes the starting winding 66 from the motor circuit. The small current drawn by the starting winding 66 is,-however,

sufficient to maintain the resistor 46 heated and the resistance thereof high.

The resistor 46 used in a working embodiment of this Overall length of housing piece 22 1.812 inches Overall width of housing piece 22 1.031 inches Overall thickness of housing piece 22 .205 inches Diameter of cavity portion 32 .937 inches Depth of cavity portion 32 .110 inches Width of groove 34 .094 inches Depth of groove 34 .110 inches Angle of groove 34 to one hole 30 degrees Overall length of contact 44 1.375 inches Overall width of contact 44 .250 inches Thickness of contact 44 .016 inches Height of how in contact 44 .094 inches Assembly of the various parts into the integrated assembly shown in FIGS. l-3 is performed by placing, for example, one contact 48b in the notches 34b and 36b of housing piece 22b to diametrically span the circular cavity portion 32b bowed upwardly as shown in FIG. 7. The resistor 46 is placed in cavity portion 32b against contact 48b. Next the housing piece 22a with the contact 48a assembled in the notches 34a and 36a to diametrically, span the cavity portion 32a and bowed away from the surface 42a is mounted on the housing piece 22b with the matching surfaces 30 thereof engaged and the contact 48a engaged with resistor surface 60a. The clip 26 is positioned on the piece 22a, and the rivets 28a and 28b are installed and headed over to secure rigidly the assembly together. The leads 24a and 24b are thus available for connection to external circuitry.

The notches 34 and 36 and mating portions of the contacts 48 serve to locate rectilinearly the latter in position with respect to the cavity 32. The securement of the two housing pieces to each other serves to complete the location and securement of the contacts and the electrical connection thereof to the resistor 46. The contacts 48 being of strip shape formed of sheet stock provide relatively flat, localized and extended area surfaces for engagement with like areas on the respective flat surfaces of resistor 46 thereby to minimize the resistance of engagement therebetween.

The structure because of its simplicity and design is economical to manufacture, requires a minimum of fasteners such as rivets or screws, and occupies a minimum of space.

While there have been described above the principles of this invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of the invention.

What is claimed is:

1. For use in selectively energizing the starting field winding of a split phase induction motor, a positive temperature coefficient resistance device being adapted to be series-connected with said starting field winding, said device comprising:

a. a multiple piece housing having matching surfaces between two of said pieces, and having a cavity which opens into said matching surfaces and which includes both a first receiving surface in spaced parallel relationship to said matching surfaces and a second receiving surface in spaced parallel relationship to said first receiving surface;

b. notch means comprising oppositely-disposed notches in said housing which open into said cavity and into said matching surfaces, for positioning each of a pair of strip contacts in said housing in rectilinear relationship to respective ones of said receiving surfaces and for providing access from 6 the outside of said housing to said cavity for a pair of electrical conductors;

c. a pair of elongated metallic strip contacts being inserted into said cavity, each being positioned proximal to one of said receiving surfaces, each having one end thereof positionally engaged with one of said notches, and each having terminal means on the other end thereof positionally engaged with an oppositely disposed one of said notches;

d. a positive temperature coefficient resistor having parallel-disposed contact surfaces, and being inserted into said cavity intermediate of said contacts; and

e. means for securing said housing pieces into fixed engagement,

said housing being formed of dielectric material in two identical pieces, said notch means includes a pair of said oppositely-disposed notches in each of said pieces, each pair of said notches including a terminal receiving notch which extends from said cavity to the outside of said housing and which is rotationally displaced about said matching surfaces from the other of said tenninal receiving notches when said housing is assembled, said electrical contacts are each of electrical conductor spring metal, are each of an elongated and generally rectangular shape, are each wider than said terminal receiving notches, are each formed with a bow intermediate the ends thereof to provide spring-loaded contact with said contact surfaces, and each include a swagable lug portion on one end thereof to provide said terminal means and to fit one of said terminal notches; a pair of insulated electrical conductors each being swaged to one of said lugs in electrical conducting contact therewith; said positive temperature coefficient resistor includes a layer of silver on each of said parallel-disposed contact surfaces, said securing means comprises a pair of holes which receive a pair of tubular rivets, respectively, and each including a head portion on each end thereof to secure said rivets to said pieces, and spring clip means having two holes therethrough spaced to match said holes in said housing pieces and being inserted between one of said housing pieces and a pair of said head portions for attaching said device to any thin and substantially flat element by sliding said spring clip thereover 

1. For use in selectively energizing the starting field winding of a split phase induction motor, a positive temperature coefficient resistance device being adapted to be seriesconnected with said starting field winding, said device comprising: a. a multiple piece housing having matching surfaces between two of said pieces, and having a cavity which opens into said matching surfaces and which includes both a first receiving surface in spaced parallel relationship to said matching surfaces and a second receiving surface in spaced parallel relationship to said first receiving surface; b. notch means comprising oppositely-disposed notches in said housing which open into said cavity and into said matching surfaces, for positioning each of a pair of strip contacts in said housing in rectilinear relationship to respective ones of said receiving surfaces and for providing access from the outside of said housing to said cavity for a pair of electrical conductors; c. a pair of elongated metallic strip contacts being inserted into said cavity, each being positioned proximal to one of said receiving surfaces, each having one end thereof positionally engaged with one of said notches, and each having terminal means on the other end thereof positionally engaged with an oppositely disposed one of said notches; d. a positive temperature coefficient resistor having paralleldisposed contact surfaces, and being inserted into said cavity intermediate of said contacts; and e. means for securing said housing pieces into fixed engagement, said housing being formed of dielectric material in two identical pieces, said notch means includes a pair of said oppositely-disposed notches in each of said pieces, each pair of said notches including a terminal receiving notch which extends from said cavity to the outside of said housing and which is rotationally displaced about said matching surfaces from the other of said terminal receiving notches when said housing is assembled, said electrical contacts are each of electrical conductor spring metal, are each of an elongated and generally rectangular shape, are each wider than said terminal receiving notches, are each formed with a bow intermediate the ends thereof to provide spring-loaded contact with said contact surfaces, and each include a swagable lug portion on one end thereof to provide said terminal means and to fit one of said terminal notches; a pair of insulated electrical conductors each being swaged to one of said lugs in electrical conducting contact therewith; said positive temperature coefficient resistor includes a layer of silver on each of said paralleldisposed contact surfaces, said securing means comprises a pair of holes which receive a pair of tubular rivets, respectively, and each including a head portion on each end thereof to secure said rivets to said pieces, and spring clip means having two holes therethrough spaced to match said holes in said housing pieces and being inserted between one of said housing pieces and a pair of said head portions for attaching said device to any thin and substantially flat element by sliding said spring clip thereover. 